Molecular sieves having a MWW framework structure are commonly referred to as a “MWW family molecular sieve material”. As used herein, the term “MWW family molecular sieve material” includes one or more of:
(i) molecular sieves made from a common first degree crystalline building block unit cell, in which the unit cell has the MWW framework topology. (A unit cell is a spatial arrangement of atoms which if tiled in three-dimensional space describes the crystal structure. Such crystal structures are discussed in the “Atlas of Zeolite Framework Types”, Fifth edition, 2001, the entire content of which is incorporated as reference);(ii) molecular sieves made from a common second degree building block, being a 2-dimensional tiling of such MWW framework topology unit cells, forming a monolayer of one unit cell thickness, preferably one c-unit cell thickness;(iii) molecular sieves made from common second degree building blocks, being layers of one or more than one unit cell thickness, wherein the layer of more than one unit cell thickness is made from stacking, packing, or binding at least two monolayers of one unit cell thickness. The stacking of such second degree building blocks can be in a regular fashion, an irregular fashion, a random fashion, or any combination thereof; and(iv) molecular sieves made by any regular or random 2-dimensional or 3-dimensional combination of unit cells having the MWW framework topology.
The MWW family molecular sieve materials are characterized by having an X-ray diffraction pattern including d-spacing maxima at 12.4±0.25, 3.57±0.07 and 3.42±0.07 Angstroms (either calcined or as-synthesized). The MWW family molecular sieve materials may also be characterized by having an X-ray diffraction pattern including d-spacing maxima at 12.4±0.25, 6.9±0.15, 3.57±0.07 and 3.42±0.07 Angstroms (either calcined or as-synthesized). The X-ray diffraction data used to characterize said molecular sieve are obtained by standard techniques using the K-alpha doublet of copper as the incident radiation and a diffractometer equipped with a scintillation counter and associated computer as the collection system. Materials that belong to the MWW family include, but not limited to, MCM-22 (described in U.S. Pat. No. 4,954,325); PSH-3 (described in U.S. Pat. No. 4,439,409); SSZ-25 (described in U.S. Pat. No. 4,826,667); ERB-1 (described in European Patent No. 0293032); ITQ-1 (described in U.S. Pat. No. 6,077,498); ITQ-2 (described in International Patent Publication No. WO97/17290); ITQ-30 (described in International Patent Publication No. WO2005118476); MCM-36 (described in U.S. Pat. No. 5,250,277); MCM-49 (described in U.S. Pat. No. 5,236,575); MCM-56 (described in U.S. Pat. Nos. 5,362,697, 5,827,491, and 5,453,554); EMM-10 (described in U.S. Pat. No. 8,110,176), EMM-10-P (described in U.S. Pat. No. 7,959,599), EMM-12 (described in International Patent Publication No. WO2010/021795), EMM-13 (described in International Patent Publication No. WO2010/014406), and an MCM-22 family material (described in U.S. Pat. No. 7,842,277). Also, UZM-8 (described in U.S. Pat. No. 6,756,030); and UZM-8HS (described in U.S. Pat. No. 7,713,513). The entire contents of said patents and applications are incorporated herein by reference.
It is to be appreciated that the MWW family molecular sieves described above are distinguished from conventional large pore zeolite alkylation catalysts, such as mordenite, in that the MWW family molecular sieve materials have 12-ring surface pockets which do not communicate with the 10-ring internal pore system of the molecular sieve.
The MWW family molecular sieves have been found to be useful in a variety of hydrocarbon conversion processes, and are especially valuable for use in a process for producing alkylaromatics, particularly ethylbenzene and cumene, or for use in a process for oligomerization of olefins, particularly for production of dimers, trimmers and tetramers of olefins, e.g., ethylene, propylene, butylene, or mixtures thereof.
There is a need to decrease crystallization times and to increase reactor throughput when synthesizing MWW family molecular sieve materials by currently available means. Prior efforts to decrease crystallization time and to increase throughput met with the problem of increased impurity formation.
According to the present invention, it has now unexpectedly been found that we can significantly avoid the above problems by the use of PAS in an improved method for synthesizing MWW family molecular sieve materials. This improved method provides a MWW family molecular sieve material product unencumbered by impurities, e.g., crystals of ferrierite, kenyaite, or other non-MWW family molecular sieve materials as identified by X-ray diffraction, with adjustment of the composition of the crystallization reaction mixture and control of the crystallization conditions, as detailed herein.